1. Field of the Invention
The present invention relates to a digitizing control apparatus for successively receiving positional data and producing NC data while tracing the shape of a model, and more particularly to a digitizing control apparatus of simple arrangement which can obtain highly accurate data in a direction normal to the surface of a model.
2. Background of the Related Art
Heretofore, there has been employed a contact-type probe as a tracer head in a digitizing control apparatus. While the contact-type probe is being held in contact with a model surface, displacement information is obtained from the model surface by the probe, and feed control data or NC data are calculated from the obtained displacement information. However, the surface of a model which is of a soft material tends to be damaged by the pressure with which the probe is held against the model.
To overcome the above drawback, there has been developed a digitizing control apparatus which has a tracer head comprising a non-contact-type detector for detecting the distance up to the surface of a model in a non-contact manner.
Unlike the contact-type probe, however, the non-contact-type detector can detect only one-dimensional displacement information at one time. In order to obtain data in a direction normal to the surface of a model, which data are required to calculate a tool offset, for example, three non-contact-type detectors are employed to determine the coordinates of three points on the model surface, and a vector in the normal direction are calculated from the coordinates of the three points. According to another attempt, a zigzag tracing path is generated, and a vector in the normal direction is calculated from the coordinates of three points that are successively measured on the tracing path.
Use of the three non-contact-type detectors is not preferred because of the required high cost. Generation of the zigzag tracing path imposes mechanical limitations such as on a feed speed, etc., results in a reduced degree of accuracy, and takes an increased period of time for digitizing.